Sierra Grande

More than 1,000 square miles undersells the field by a long way. The Park Service measures the Raton-Clayton volcanic field at nearly 8,000 square miles, from Trinidad in Colorado to Clayton, with some hundred vents built over the last nine million years. Sierra Grande is among its biggest single works. It is the easternmost Cenozoic volcanic field in the United States, and the flat-topped mesas around Raton are older lava caps left standing as the softer country around them wore away.

What the plaque says

Official Scenic Historic Marker Sierra Grande Largest extinct volcano in northeastern New Mexico, Sierra Grande rises to an elevation of 8,720 feet, one of many volcanoes, cinder cones, and flows that cover more than 1,000 square miles of area in northeastern New Mexico and southeastern Colorado eastward to the Oklahoma state line.

Where it stands

Worth the stop nearby

• Capulin Volcano National Monument — 6.6 mi
  A cinder cone you can drive to the top of, rising more than a thousand feet from the high plains east of Raton, whose lava broke out of its foot rather than its crater.

More markers nearby

• Sierra Grande — 6.5 mi
• Capulin Volcano National Monument — 6.8 mi
• Capulin Volcano National Monument — 8.0 mi